This invention relates to an integral field and commutation magnet for a DC brushless motor, and an apparatus and method for making it.
In direct current motors, a commutation device properly commutates the current in the stator winding or windings at appropriate points in the rotor's rotation. Therefore, the commutation arrangement must be correctly located with respect to the angular position of the rotor so that the commutation arrangement accurately effects switching of the current windings at the proper positions of the rotor relative to the stator.
Various types of cummutation arrangements have been used in DC motors having permanent magnet rotors. These energize a new stator winding or reverse the current in the stator winding each time the rotor rotates to preselected angular positions or commutation points. Hall effect devices have provided a successful means for sensing commutation points to control a semiconductor switching circuit that switches or reverses the stator current. Commutation magnets have been affixed to the rotor to alter the state of the Hall device or devices as a magnet repeatedly rotates into and out of proximity with a Hall device.
In the past, when permanent magnet commutation magnets have been employed, distinct from the rotor permanent magnets, or field magnets, these have been separately made and magnetized and separately mounted on the rotor in the correct angular relationship to the rotor magnets. This has meant molding the commutation segments of a commercially available plastic permanent magnetic material, for example, and subjecting each segment to a magnetic field of the appropriate intensity and direction, either before or after the magnets had been attached to the rotor.